Dibasic acid esters and method for producing them



Patented Nov. 13, 1951 DIBASIC ACID ESTERS AND METHOD FOR PRODUCING THEM Paul VQSmith, Jr., Westfield. N. J., assignor to Standard Oil Development Company, a corporation of Delaware N Drawing. Application October 1, 1948, Serial No. 52,428

8 Claims.

This invention relates to a new class of compounds which have been found to be particularly suitable for use as synthetic lubricants because of their low pour points and high viscosity indices.

In the lubricant art, considerable progress has been realized in recent years in the production of lubricants characterized by one or more specific properties and adapted for particular uses. In the main, this progress can be attributed to two developments: the first, new refining procedures, and the second, addition agents capable of imparting particular properties to available lubricants. Thus, viscosity index improvers and pour depressants are added to automotive lubricanis to render the lubricants more adaptable to wide changes in temperature conditions, while other agents are added to improve the load carrying properties of a lubricant which is to be employed, for example, under extreme pressure conditions.

Recently, in an effort to obtain superior lubricants endowed with specific and superior characteristics, a new field has been explored, namely the synthesis of lubricants from various materia s. Esters represent one class of materials which have attracted unusual interest as synthetic lubricants. In general, they are characterized by higher viscosity indices and lower pour points than mineral oils of corresponding viscosity. The esters described in the present specification have been found to exh bit very low pour points and high viscosity indi es. Lubricants possessin such properties are of spe ial value in the lubrication of engines which are subjected to high temperatures such as combustion turbine engines. particu arly those of the prop-jet" type. Mineral oil lubricants containin added viscosity index improvers, thickeners or other highly nonvolatile additives are undesirable for use in su h engines because of the tendency to leave a residue which accumu ates and interferes with the operation of the engine. A synthetic lubricant of the type described in the present specification is especial y adapted to use under such conditions, since t e lubricant contains no additives and thus tends to leave no residue upon volatilization.

The new compounds of the present invention which have been found to be particularly suitable for use as lubricating oils are complex esters prepared by reacting one mol of a dibasic acid with one mol of a glycol in such a manner that a half ester is formed, after which the terminal hydroxyl and carboxyl groups are esterified with a mono basic acid and monohydric alcohol, respectively.

More precisely, the new class of compounds may be defined by the following general formula:

COOR" where R is an aliphatic hydrocarbon radical, straight chain or branched, saturated or unsaturated, containing 0 to 26 carbon atoms, or it may be an organic radical consisting of a series of saturated aliphatic hydrocarbon radicals linked by one or more atoms of oxygen or sulfur, or both oxygen and sulfur, provided there are at least two carbon atoms between each pair of oxygen or sulfur atoms, and provided further that the total number of carbon, oxygen and sulfur atoms is from 3 to and the total number of sulfur atoms is not greater than 2. R of the formula represents a glycol radical and may consist of a saturated aliphatic hydrocarbon group, straight chain or branched, containing 2 to 18 carbon atoms, or it may be a series of saturated aliphatic hydrocarbon radicals linked by oxygen or sulfur atoms, or by both oxygen and sulfur atoms, provided there are at least two carbon atoms between each carboxyl group and the nearest oxygen or sulfur atoms and at least two carbon atoms between each oxygen or sulfur atom in the chain, and provided further that the total number of carbon, oxygen and sulfur atoms in the entire R radical is from 5 to 80 and the number of sulfur atoms is not greater than 2. R" of the formula represents a monohydric alcohol residue which may be a saturated or unsaturated aliphatic hydrocarbon radical, either straight chain or branched, containing 1 to 20 carbon atoms, or it may be a series of saturated aliphatic hydrocarbon radicals, straight chain or branched, interlinked by oxygen or sulfur atoms, or both oxy en and sulfur atoms, the total number of carbon, oxygen and sulfur atoms being from 4 to 20. The maximum number of oxygen or sulfur atoms or both in the radical R" is not greater than 5, and there is a chain of at least two carbon atoms between the acid radical and the first oxygen or sulfur atom and a similar chain of at least two carbon atoms between each pair of oxygen or sulfur atoms in the radical. R of the formula represents an aliphatic hydrocarbon radical, straight chain or branched, saturated or unsaturated, containing 1 to 22 carbon atoms, or it may represent a series oi aliphatic hydrocarbon radicals interlinked by 1 to 5 oxygen atoms, there being at least two carbon atoms between each pair of oxygen atoms and at least one carbon atom between the carboxyl group and the nearest oxygen atom, the total number of carbon and oxygen atoms in the radical being from 3 to 22, or it may represent an organic radical. consisting of an aliphatic hydrocarbon chain containing a single interlinked sulfur atom which is separated from the carboxyl group by at least one carbon atom, the total number of carbon and sulfur atoms in the radical being from 3 to 22. The molecular weight of the entire ester should be at least 300 and the viscosity at 210 F. should not be greater than 150 seconds (Saybolt) to provide a product having lubricating properties.

Among the various components of the complex esters of the present invention certain preferences may be pointed out as giving the optimum of desired properties from thestandpoint of service as a lubricant. The preferred dibasic acids are the straight chain dibasic acids of the para!- finic group having from 6 to 10 carbon atoms per molecule. The preferred monohydric alcohols are the aliphatic primary alcohols, whether straight chain or branched, containing no oxygen or sulfur atoms and having from 6 to 10 carbon atoms per molecule. The preferred monobasic acids are the fatty acids containing 2 to 10 carbon atoms per molecule.

The complex esters of this invention may be prepared by reacting one molecular proportion of a dibasic acid with one molecular proportion of a glycol under esteriflcation conditions until only one molecular proportion of water oi. reaction is produced, and thereafter esterifylng the unreacted carboxyl and hydroxyl groups with a monohydric alcohol and a monobasic acid, respectively. A method suitable for carrying out the process in detail will be described below in connection with specific examples.

Illustrative examples of the dibasic acids which may be employed in the synthesis of the complex esters or the present invention are the following:

Oxalic acid Malonic acid Succinic acid Glutaric acid Adipic acid Pimelic acid Suberic acid Azelaic acid Sebacic acid Brassylic acid Pentadecanedicarboxylic acid Tetracosanedicarboxylic acid (fl-C24 alkenylsuccinic acids Diglycolic acid Thiodiglycolic acid The C4C2-i alkenylsuccinic acids listed above are prepared by condensing olefins or mixtures of olefins with maleic anhydride.

The glycols employed in preparing the esters of the present invention include ethylene glycol and any of the paraflinic homologues of the same containing up to 18 carbon atoms. These may include, for example, ethylene glycol, propylene glycol, butylene glycols, pinacone, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, and the like. Since the glycols may also contain oxygen or sulfur atoms, compounds such 4 as dlethylene glycol, triethylene glycol, the polyethylene glycols of the formula HO (CHzCHzO) .CHzCHzOH where n is 1 to 26, and the polypropylene glycols 01 the general formula where either R1 or R2 is a methyl group and the other is hydrogen, and where n is 1 to 20, may likewise be employed. Glycols containing sulfur atoms in thioether linkages may also be employed, and these include such compounds as thiodiglycol and 1,2 bis(2 hydroxyethylmercapto) ethane. There also may be used glycols containing both oxygen and sulfur in similar linkages; such a compound is bis- [2-(2-hydroxyethoxy) ethyl] sulfide.

The monohydric alcohols employed are typified by the following:

Methyl alcohol Ethyl alcohol n-Butyl alcohol n-Hexyl alcohol n-Octyl alcohol Z-ethylhexyl alcohol Cetyl alcohol Oleyl alcohol Ethylene glycol mono-n-butyl ether Ethylene glycol mono-2-ethylbutyl ether Ethylene glycol mono-Z-ethylhexyl ether Ethylene glycol mono-tert.-octyl ether p-n-Butylmercaptoethanol p-tert-Octylmercaptoethanol fl-n-Dodecylmercaptoethanol Diethylene glycol monon-butyl ether Diethylene glycol mono-2-ethylbutyl ether Diethylene glycol mono-2-ethylhexyl ether Propylene glycol mono-butyl thioether Propylene glycol mono-tert.-octyl thioether Propylene glycol mono-n-dodecyl thioether n-Butylmercaptoethoxyethanol tert.-Octylmercaptoethoxyethanol n-Dodecylmercaptoethoxyethanol n-Butylmercaptopropoxypropanol tert.-Octylmercaptopropoxypropanol n-Dodecy1mercaptopropoxypropanol Propylene glycol mono-n-butyl ether Dipropylene glycol monomethyl ether Dipropylene glycol monoethyl ether Dipropylene glycol mono-n-butyl ether Tripropylene glycol monomethyl ether Tripropylene glycol monoethyl ether Tripropylene glycol mono-n-butyl ether Propylene glycol monoisopropyl ether Dipropylene glycol monoisopropyl ether Tripropylene glycol monoisopropyl ether Many of the above listed ether alcohols, formed by the reaction of ethylene oxide or propylene oxide with aliphatic alcohols, are known in the industry as Dowanols, Carbitols, or Cellosolves."

A group of alcohols especially adapted for use in connection with the present invention are the sc-called "0xo alcohols, prepared by the reaction of carbon monoxide and hydrogen upon the olefins obtainable from petroleum products. Materials such as diisobutylene and C1 olefins are suitable for this purpose; also higher molecular weight olefinic materials are sometimes employed. The alcohols obtained in this manner normally have a branched chain structure.

6 Among the monobasic acids which may be emmore water collected. The mixture was washed ployed in the preparation of the esters of the with three 100 ml. portions oi saturated sodium present invention. the following m y be listed as carbonate solution and one 100 ml. portion of illustrative: water. After drying over "Drlerlte" '(anhydrous Acetic acid calcium sulfate). the material was filtered and n i l acid stripped to a bath temperature of 200-225 C. at Butyric acid I a pressure of about 5 mm. V leri a id The results of tests of various properties of Caproic acid esters prepared by the above general method are Caprylic acid shown in Table I.

Table I i mash Kinematic Viscosity ASTM' Component oi Ester Point MW PM! P 100 F. 210 r. on Index 5 again: tad"--. l gg fi flfl g 355 45.120 0.050 0.1m n1 so 2-EthylhsxanoL. Adipic acid r 400 satao 1.242 0.03s 14: -8s

no less; use 0.0m 1m -as 400 38.510 1.055 cm 155 -is 410 um 10.40:; am no -ss (i -(Z Alkenylsuccinlc acid.. 'i'figgfi fifi'fk 515 62.155 0.049 0.004 125 ss Metl/yi alcohol C Alkenylsucclniacid g 'figi fififf (3 390 57.952 am am 12s Met yl alcohol..- Sehscic acid igg flgggtgf ff; 300 25.410 5.651 ass-1 162 15 C15- 1] "0X0" 8100b Laurie acid The above data indicate that the esters consti- Palmitic acid tilting the subject-matter of the present invention stearic acid possess characteristics, particularly with regard Oleic acid to viscosity index and pour point, which indicate p-Methoxypropionic acid their suitability for general use as lubricating oils p-Ethoxypropionic acid and particularly for use where the use or additives p-Tert-octoxypropionic acid is not desirable. The esters of the present invenp-Ethylmercaptopropionic acid tion may also be blended with mineral lubricating fl-Tert-- y m pwpropionic acid oils to give lubricants or improved viscosity index fi-Tert.dodecylmercaptopropionic acid and pour point.

If desired, various addition agents may be inwhat is claimed is: corporated in the esters of the present invention A5 a new composition compound for the purpose of improving their properties of the formulawith respect to their usefulness as lubricants. coon" For example, antioxidants, viscosity index improvers, thickeners, pour depressants, dyes, etc., may be added.

Data will be given below showing the propern' ties of several examples of complex esters within m the scope of the present invention indicating the adaptability of these esters to lubricating WhereRis an aliphatic hydrocarbon radical conservice. All of these esters were prepared by a taining 2 to 8 carbon atoms in a straight chain general esterification method which was carried between the COO groups, where R is a radiout in detail as follows: In a 1-liter round botcal of the formula -(CH:CH:O) nCH2CH:-, tomed reaction flask, fitted with a reflux conwhere n is an integer from 1 to 7; where R" is denser and water trap, was placed a charge conan alkyl group containing 1 to 19 carbon atoms; sisting of 1 mol of dibasic acid, 1 incl oi glycol, nd Where R' is an alkyl group containing 3 to 7 4.5 gr. of p-toluenesulfonic acid monohydrate, carbon atoms.

and 100 ml. of toluene. The mixture was re- 2. A composition according to claim 1 in which fluxed until exactly one mol of water was col- Ris aradical containing-i carbon atoms.

lected in the trap. Then, after cooling, 1 mol of 3. A composition according to claim 1 in which monohydric alcohol was added and the reaction R is a radical containing 4 carbon atoms and R" continued until no more water collected in the is a 2-ethylhexyl radical. trap. One mol of monobasic acid was then 4. Acomposition according to claim 1 inwhich added and the reaction continued until again no R is a radical containing 4 carbon atoms, R" is a 2-ethylhexyl radical. and R'" is an n- -D Y radical.

5. A composition according to claim 1 in which R is the radical (CH2CH20) :CHaCHz- 6. A composition according to claim 1 in'which R. is the radical (CH2CH2O) :CHaCI-Ia- 7. A method which comprises reacting one molecular proportion of a polyethylene glycol with one molecular proportion of adipic acid, under conditions which provide for the removal of water formed in the reaction from the reaction zone, until only one molecular proportion of water of reaction is formed and removed, and thereafter adding one molecular proportion of 2-ethylhexanol to the reaction mixture and continuing the esteriflcation reaction until no more water is formed, and thereafter adding one molecular proportion or n-caproic acid and continuing the esterification reaction until again no more water of reaction is formed.

8. A method according to claim '7 in which the glycol employed is triethyiene glycol.

PAUL V. sm'm, Jl.

REFERENCES CITED Y The following references are of record in th file of this patent:

UNITED STATES PATENTS Number Name Date 1,786,404 Young Dec. 23, 1930 2,035,528 Brubaker Mar. 31, 1938 2,073,031 Sly Mar. 9, 1937 

1. AS A NEW COMPOSITION OF MATTER A COMPOUND OF THE FORMULA- 